your post is extremely long so forgive me if I had to start skimming through. A few things you should do. 1) if you plan on pulling a camper, do as you mentioned in the first chapter of this novel and install a tranny cooler . 2) flush your coolant system with clean water from a garden hose in reverse direction via the hvac hook ups. Be sure to do it with low pressure and gradually increase to about 1/3 strength. Also be sure to get that radiator really clean inside, and inspect for deposits, sometimes people use tap water to fill or mix their coolant and that can leave mineral deposits or build ups. Use distilled water whenever possible. Speaking of coolant....... if you mixed your coolant "rich" meaning you used more antifreeze then water, it isnt that big a deal. 3) the last thing make sure you get all the air pockets out. There are plenty of videos on you tube of how to do this, but dont assume that its good, make sure. Also make sure your hoses are not collapsing.
This is a personal preference for me and not inline what GM says to do. When I replaced my water pump and was having cooling issues. I switched to regular prestone antifreeze in place of the dextron. I saw what that stuff did to the intake gaskets of my daughters malibu when I replaced the intake and head gaskets, and I wont use it ever again. Im sure others find it fine.